With the continuous development of wireless communication technology, board to board connectors are becoming more and more widely used in wireless system module interconnection, such as communication base station, RRH, repeater, GPS devices, and other similar applications. Three major trends of wireless devices are smaller dimension, lower cost, and easier installation. For a board to board connection, the market also requires them to be smaller, cheaper and more modularized.
In particular, there are already on the market and in the prior art examples of connection assemblies dedicated to the telecommunications sector for cellular radiotelephony infrastructures. In fact, the trend in this market is to minimize the losses of the RF (radiofrequency) part in order to reduce the amplifying elements of the base stations. For this, on the one hand, the actual radio part of the stations is being increasingly relocated as close as possible to the transmission-reception antennas, in the RRU/RRH transmitter modules, and on the other hand, the RF leads internal to the radio unit are being replaced by direct interconnections.
So-called board-to-board connections have thus been developed according to the successive generations of the last decade.
A first generation of connection assemblies is thus known, for directly interconnecting boards, for example marketed under the names SMP, SMP-Com, MMBX from Radiall. Such connection assemblies respectively consist of a first socket of snap-fitting (or “snap”) type, a second socket of “sliding” (or smooth bore) type with a guiding cone (“slide on receptacle”), and a connection coupling called adaptor, with the first and second sockets respectively fastened to the ends thereof. The connection is therefore made blind by the re-centring of the connection coupling by means of the guiding cone of the sliding socket. The major drawback is the great limitation on the axial and radial misalignments allowed for these connections. In practice, the axial misalignment is limited to a few tenths of a millimetre, of the order of 0.3 mm to 0.6 mm, in order to keep the impedance of the coaxial line at a value equal to 50 Ohm. The radial misalignment is obtained by a rotation of the coupling in the groove of the snap-fitting socket, this rotation being in fact relatively small to avoid damaging the central contact and the elastic means with which the connection coupling is provided.
A second generation of connection assemblies is also known, for example marketed under the names SMP-MAX by the company Radiall or else marketed under the names MBX by the company Suhner or else marketed under the name AFI by the company Amphenol RF, or else marketed under the name Long Wipe SMP and P-SMP by the company Rosenberger.
Such connections, to link two printed circuit boards, generally consist of three elements, namely: a first socket of sliding type, a second socket with snap-fitting or of retention type and a connection coupling with the first and second sockets respectively fastened to the ends thereof.
The first and second sockets are conventionally made of brass and have no elastic functions. The connection coupling is typically made of an expensive noble elastic metallic material, for example CuBe2 or BZ4, and provided at each of its ends with elastic means (petals and slots for example) that cooperate with the first and second sockets.
This second generation of connections made it possible to increase the accepted axial misalignment value. Thus, as described in particular in the patent application WO 2010/010524, this increase can result from an impedance compensation at the coupling end, which makes it possible to obtain a trade-off in mechanical and electrical efficiency regardless of the inclination of the coupling relative to the sockets.
All the known board-to-board connections do however present a significant number of drawbacks.
On the one hand, because the couplings of these connections have elastic means generally consisting of petals at their ends, they can be fragile. Thus, it is commonplace, when connecting blind, for the coupling to be damaged when it comes into contact with the guiding cone of a sliding socket.
On the other hand, the configuration of the connections does not make it possible to obtain a sufficiently great radial and/or axial misalignment. In particular, significant rotation angles, typically greater than 3.5°, cannot be reached without causing an undesirable permanent deformation of the elastic means of the coupling. This permanent deformation causes a significant degradation of the electrical performance levels (electrical continuity), which de facto limits the radial misalignment allowed, in particular for a small distance between boards to be connected.
At last, the cost of producing these connections is relatively high, thus constituting a brake for this type of market. In particular, producing the connection coupling from a noble material, in particular when the coupling has a significant length, and producing possible slots in this coupling results in not-inconsiderable production costs.
In the case of the connection assembly according to the patent application WO 2010/010524, said connection needs in fact three different pieces which are connector elements, namely two receptacles which are each soldered on a PCB and one elongated rigid coupling to connect together the two receptacles. When applied in massive board to board connection, it might result of this type of solution a very big insertion force and make the connection between two PCB difficult.
Another current solution to realize a board to board connection is described in U.S. Pat. No. 6,231,352B1. Though it adopts only one connector to realize the board to board connection, it still needs soldering process to fix each longitudinal end of the connector on the PCB. This solution is not convenient for maintenance, when applied in different board to board heights. Besides, once the maintenance is done, the connector needs to be redesigned, with an impedance that is not necessarily well controlled. This solution is not good for applications which require some modularization and standardization.
There is therefore a need to further improve the board to board connections, in particular by providing the minimum of pieces required for the connection, by allowing an installation with less solder in order to improve the installation efficiency, an easy maintenance with the possibility to easily extract the connection, a certain misalignment tolerance, a controlled impedance line with good RF performances, the possibility of an easy standardization and modularization and, at low cost.
The invention aims to address all or part of these needs.